function getData(endpoint) {
  return new Promise((resolve,reject) => {
    const xhr = new XMLHttpRequest();

    xhr.open('GET', endpoint);

    xhr.onreadystatechange = function () {
      if (this.readyState === 4) {
        if (this.status === 200){
          resolve(JSON.parse(this.responseText));
      } else {
        reject('出现了一些错误');
      }
    }
  };

  setTimeout(() => {
    xhr.send();
  }, Math.floor(Math.random() * 3000) + 1000);
});

}

getData('./movies.json')
  .then(movies => {
    console.log(movies);
    return getData('./actors.json');
  })
  .then(actors => {
    console.log(actors);
    return getData('./directors.json');
  })
  .then(directors => {
    console.log(directors);
  })
  .catch(error => {
    console.log("出现了问题");
  });

  
  
